Maize Genomics and Genetics 2025, Vol.16, No.1, 20-33 http://cropscipublisher.com/index.php/mgg 22 leaf chlorophyll content, leading to a decline in crop productivity and yield stability at very high densities (Zhang et al., 2021). Additionally, while higher planting densities can increase canopy apparent photosynthesis (CAP) and biomass, they may also lead to greater competition for light, water, and nutrients, which can negatively impact yield if not managed properly (Wei et al., 2019). Moreover, the relationship between planting density and photosynthesis is complex. For instance, while medium planting densities (e.g., 105 000 plants/ha) have been shown to significantly increase grain yield by up to 20.32% compared to lower densities, further increases in density do not necessarily lead to additional yield benefits and may even result in yield reductions for some cultivars (Yan et al., 2019). This suggests that there is an optimal planting density that maximizes photosynthetic efficiency and yield without causing excessive competition among plants. 3.2 Advantages and disadvantages of high-density planting and its impact on yield High-density planting has several advantages, including increased IPAR and improved resource use efficiency, which can lead to higher grain yields under optimal conditions. For example, a study found that increasing planting density combined with a reduced nitrogen rate enhanced nitrogen partial factor productivity (NPFP) by 24.7% and maize grain yield by 6.6% compared to conventional practices (Figure 1) (Du et al., 2021). This indicates that high-density planting, when managed with appropriate nutrient inputs, can be beneficial for achieving high yields. Figure 1 N uptake, N harvest index and N partial factor productivity of maize (NPFP) under different planting treatments in 2017 and 2018 (Adopted from Du et al., 2021) Image caption: Error bars indicate standard errors of replicates. Means followed by the same letter are not significantly different among different planting treatments at P < 0.05 (Adopted from Du et al., 2021) However, high-density planting also has its disadvantages. It can trigger a shade avoidance response, leading to increased plant height and ear height, which can result in lodging and yield loss (Jafari et al., 2021). Additionally, excessive planting density can exacerbate competition for resources, reducing photosynthetic capacity and yield stability. For instance, in semiarid environments, pursuing too high planting density is not advisable as it can lead to reduced precipitation use efficiency (PUE), radiation use efficiency (RUE), and nitrogen use efficiency (NUE) (Zhang et al., 2021). Therefore, while high-density planting can be advantageous, it requires careful management to avoid negative impacts on yield. 3.3 Regional variations and cultivar adaptability to optimal planting density The optimal planting density for maize can vary significantly depending on regional conditions and the specific cultivars used. In semiarid regions, moderate planting densities are recommended to stabilize grain yield and ensure sustainable agricultural practices. Density-tolerant cultivars, such as Zhengdan958 and Xianyu335, have shown better canopy structure, photosynthetic capacity, and yield stability under varying planting densities (Zhang et al., 2021). This highlights the importance of selecting cultivars that are well-adapted to the specific environmental conditions of the region.
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